There's no pat answer for this.
At first, we say if you get a PS under 150, to stall, don't feed and test again in 20-30 minutes but once you have a little more data, it becomes more of a judgement call
You gradually DO want to shoot lower numbers, but every time, you have to ask yourself:
Am I able and willing to test as often as necessary for as long as necessary?
Do I have plenty of supplies (strips, various carb foods, Karo/honey/syrup)?
How comfortable am I with understanding how to "steer" numbers?
It's also a good idea to have the "How to deal with hypo's" information printed out and someplace you can get it if you need it. The message board has occasionally had a problem when people couldn't get signed on